What punishment would Anakin have faced if the Jedi Council had found out he slaughtered the village of Sand People?
The question says it all. Padme was no snitch. Yoda shrugged off Qui-Gon's Force Ghost screams. Obi-Wan apparently has no connection through the force to his Padawan. The entire Jedi Council is oblivious. What say you? Would he have been executed? Expelled from the order? Locked in a Jedi prison? High Fived?
The penalty for disobeying a direct order from the Council, the penalty for having a secret marriage, the penalty for having a secret child all seem to be the same: Expulsion from the Jedi Order. I think we can reasonably say that murdering dozens of sentients would carry much the same punishment.
As to whether Anakin would face further censure, either from the Jedi or the civil authorities, the answer is a solid no. The Sandpeople aren't considered to be "people" on Tatooine (killing them isn't actually a crime) and the fact that he killed them while in a compulsive rage would act in his favour in terms of a "temporary insanity" plea. Even assuming you could convince the authorities on Coruscant to prosecute someone for something that's not a (local) crime, his mentor, the Chancellor has the Senate and the Judiciary tucked away in his top pocket and would prevent Anakin from facing criminal justice.
So, expulsion.
In addition to the repercussions mentioned by Valorum there is something else there one needs to consider. Even though the Republic does not see the Sand People as people, the Jedi are different there as they are still living beings.
That said, there is a great likelihood that a different punishment would be dished out. Similar to what was done to Barriss Offee. Jedi who fall to the Dark Side also not only get expelled but in some cases get imprisoned so that they can't do much more damage. This was mentioned in the Clone Wars at least once that there are even Jedi prisons.
Thus with Anakin's great skill there is also a not-so-low probability that he would, instead of being expelled, have been thrown into that prison in the hopes of having him do not more damage or even healing him and bringing him back to the Light.
Given how the Jedi philosophy is all about peace and harmony, I think there is only one penalty for grievous crimes - being kicked out.
My impression as well is that there are no real 'federal' laws in the Republic, and everything is based on local / planetary law. The laws of Tatooine would then apply.
While I agree with the answer Thomas gave, another one to consider, since the Jedi won't execute him, is the ability "Sever Force" on Anakin. Not sure if there are any Jedi remaining during those times that would even know this ability, let alone one skilled enough in it to perform it on someone as powerful in the force as Anakin.
